I am knitting cuff-to-cuff vest from Creative Knitting September 2010 publication. On the Diamond Key I am to use it shows a blacked out st and this refers to no stitch. Would this mean that I slip that stitch to the right hand needle and then knit or purl the next stitch? Thanks

When I have seen "no stitch" indicated in a chart it has meant either you have decreased in a previous row or will increase in a future row and is a placeholder. So I have just knitted the next square in the row as if the "no stitch" was not there at all, in other words do not slip. If you were to slip a stitch, I always assume that will be indicated somewhere in the chart or pattern instructions.

No stitch on a chart means 'there's no stitch on your needle for this box so skip it and go to the next box'. The squares represent actions, not stitches, so if there's a no stitch square, there's no action.